In the harvesting of certain produce, such as fresh heads of lettuce, it is desirable to wrap and seal the heads of lettuce in the field, in order to preserve them and to avoid deterioration as they are handled and shipped to market. As of the present time, this wrapping and sealing is done mostly by hand, with efforts at automation up to the present time having been sporadic and ineffective.
Accordingly, a principal object of the present invention is to simplify and automate the wrapping and sealing of fresh lettuce heads, other produce, and even other objects.
In accordance with one important aspect of the present invention, it has been determined that a certain type of valve, known as an iris valve, and which is normally used for the flow control of grain and the like, is particularly well suited for inclusion in systems for wrapping and sealing objects, such as fresh heads of lettuce. These iris valves involve the use of two open circular members which are mounted adjacent one another, and which have a tube of cloth or other fabric material with one end of the tube being secured to each of the two open circular members. When the two discs are aligned so that the cloth tube is not twisted, it is open and hangs down as a double cylinder from the two open circular members. These two circular members are mounted for rotation relative to one another, and as one of them is rotated relative to the other, the tube is gradually twisted and closed until it is finally closed completed. In this way, when the iris valve is used to control the flow of wheat or other granular material, for example, the flow may be gradually shut off as one of the two open circular members is rotated relative to the other.
The discs come in various sizes up to 12 inches or so in diameter, and a head of lettuce or other similar sized object will easily fit through the iris valve when it is opened, and be supported by it when it is closed or substantially closed.
In accordance with an important aspect of the present invention, an iris valve of the type described above, including a fabric tube, is employed in the wrapping and sealing of heads of lettuce or the like by initially dispensing a sheet of thin plastic wrapping material across the upper surface of the iris valve, and then placing the object to be wrapped on top of the valve, with the plastic layer underneath, between the object and the valve. The valve is then slowly opened so that the object slides down through the valve and engages a support (which may be another iris valve) and the upper iris valve is then drawn closed to pull the plastic sheet material over the upper surface of the object to be wrapped. The fabric tube also rotates as it is closing, thus assisting in wrapping the plastic film around the object. The plastic material is then sealed, preferably with a heat sealing member, either above the iris valve where the plastic sheet material has been drawn together, or immediately below the surface of the iris valve.
Additional features of the invention include the following:
(1) The use of multiple stations either movable or stationary, so that the object may be loaded at one station, and wrapping and sealing occurs at another station.
(2) The use of a rotating carousel unit having multiple stations to implement the wrapping and sealing function, while not slowing down the loading and depositing function which may be accomplished by the worker at his own pace.
(3) The use of automatic controls for opening and closing the iris valve or valves.
(4) The use of conveyor belts to facilitate carrying the wrapped objects away from the wrapping and sealing station and to a packaging location.
(5) The use of automatically actuated plastic sheet cutting arrangement, either of the mechanical cutting or of the hot wire type.
(6) The use of automatically actuated heat sealing arrangements, either by a hydraulic cylinder operating a heated element onto the upper surface of the plastic material above the upper valve, or by mating V-shaped sealing elements moving inwardly below the upper iris valve.
(7) The use of the second iris valve for controllably releasing the object into a conveyor belt or other receptacle following completion of the wrapping and sealing operation.
(8) The multi-station carousel type arrangement may include a series of iris valves mounted at an angle relative to the horizontal, to facilitate loading the heads of lettuce or other produce at one side, and providing sufficient elevation on the other side to accommodate a pair of overlying iris valves at the wrapping and sealing station, with space for a conveyor belt or other receptacles below the wrapping and sealing station.
Other objects, features and advantages of the present invention will become apparent from a consideration of the following detailed description and from the accompanying drawings.